This application is a 371 of PCT/GB99/00747 filed Mar. 18, 1999.
The present invention relates to improvements in the field of variable focus optical devices, in particular variable focus lenses, for example of the type in which the optical power of the lens is variable by varying the volume and/or pressure of a transparent fluid within a transparent envelope.
Variable focus lenses are known and have been described for example in GB 2183059, GB 2184562 and WO96/38744. However, to date, despite the many examples of variable focus lenses described in the prior art, none have achieved widespread commercial acceptance as an alternative to fixed-focus ground glass or plastic lenses.
It is believed that the failure of known variable focus lenses to gain commercial acceptance is due to a number of factors. For example, many known such lenses suffer from leakage of the fluid from the envelope in use. Furthermore, many known such lenses suffer from poor optical quality due to the mounting arrangement of the flexible membrane and/or the material chosen for the membrane. A further contributor to the poor optical quality of known lenses has been the fluid selected to fill the envelope, which has had a less than optimal transparency or homogeneity of refractive index. An additional reason for the non-acceptance of known lenses has been their complex and bulky configuration which has lead to a poor aesthetic effect, for example when the known lenses have been mounted in spectacles, and has also increased the cost of such spectacles to a level which is not competitive with traditional fixed-focus lenses.
The present invention seeks to provide a variable focus lens and a method of making a variable focus lens, embodiments of which overcome at least some of the problems of known variable focus lenses, whereby a more commercially attractive product can be achieved. It also seeks to provide eyewear incorporating variable focus lenses.
According to an invention disclosed herein, there is provided a variable focus lens comprising a transparent envelope at least partially defined by a flexible, transparent membrane and containing a transparent fluid, a frame member engaging one face of the flexible membrane and a ring member engaging an opposite face of the flexible membrane, the ring member and the frame member being urged towards each other by retaining means, wherein the respective surfaces of the frame member and the ring member that engage the flexible membrane are substantially complementary and profiled so as to cause a peripheral region of the flexible membrane to change direction more than once.
It has been realised by the applicant that, in order to obtain a high optical quality of the membrane, the membrane should be held under tension at all times. Furthermore, it has been found by the applicant that the membrane, when under tension, and particularly when formed of preferred materials such as Mylar tends to form its own seal against the frame member or ring member.
The profiles of the engaging surfaces of the frame member and the ring member allow the flexible membrane to be retained under tension on the frame member simply by the action of the engaging surfaces. In this way the construction of the variable focus lens is considerably simplified in comparison to known such lenses.
The profiles of the engaging surfaces may be stepped or comprise one or more projections and complementary recess(es). The portions of the engaging surfaces substantially perpendicular to the plane of the unstretched membrane will tend to frictionally engage the membrane as the ring member is urged towards the frame member by the retaining means. Such frictional engagement will tend to stretch the membrane on the frame member, ensuring that the membrane is under tension.
In a particularly advantageous arrangement, the engaging surfaces comprise at least one oblique surface which increases in radial extent towards the frame member. In this way, as the ring member is urged towards the frame member by the retaining means, friction between the oblique surface of the ring member and the flexible membrane tends to urge the periphery of the membrane radially outwardly, thereby increasing the tension in the membrane, i.e. stretching the membrane.
The ring member and frame member may be of a material or materials which is/are sufficiently rigid to positively interengage with each other and to ensure that the ring member and frame member can maintain the flexible membrane under tension. The material of the ring member and frame member is preferably also lightweight to facilitate the incorporation of lenses described herein in spectacles. Thus, the ring member and frame member may be made, for example, of a high impact resistant plastics material, or of aluminium, or of titanium.
It is generally advantageous to maximise the friction between the engaging surfaces and the membrane, not only to maximise the stretching effect described above, but also to ensure that the membrane is securely held by the ring member and the frame in the assembled lens. Preferably therefore, at least one of the surfaces is a high friction surface.
This in itself is believed to be new and thus according to an invention disclosed herein there is provided a variable focus lens comprising a transparent envelope at least partially defined by a flexible, transparent membrane and containing a transparent fluid, a frame member engaging one face of the flexible membrane and a ring member engaging an opposite face of the flexible membrane, the ring member and the frame member being urged towards each other by retaining means, wherein the respective surfaces of the frame member and the ring member that engage the flexible membrane are substantially complementary and at least one of the surfaces is a high friction surface.
For example, one or more of the frame member and the ring member may be made of a material having a high coefficient of friction at its surface. Alternatively, at least one of the engaging surfaces may have been roughened or expanded to increase its surface friction.
In a preferred arrangement, however, at least one of the engaging surfaces is provided with a coating of high friction material. A particularly preferred material for this coating is rubber or a synthetic elastomer, as this has been found by the applicant to engage well with the preferred materials for the membrane, such as Mylar.
A further advantage of providing at least one of the engaging surfaces with a coating of rubber or synthetic elastomer is that the rubber or elastomer tends to form a high integrity fluid seal at the interface between the engaging surface and the membrane.
Thus, according to an invention defined herein there is provided a variable focus lens comprising a transparent envelope at least partially defined by a flexible, transparent membrane and containing a transparent fluid, a frame member engaging one face of the flexible membrane and a ring member engaging an opposite face of the flexible membrane, the ring member and the frame member being urged towards each other by retaining means, wherein at least one of the engaging surfaces is provided with a coating of rubber or synthetic elastomer.
It has been found by the applicant that the coating need only be thin, in order to achieve an advantageous effect. For example, the coating may have thickness of less than 100 xcexcm, or less than 50 xcexcm, or less than 20 xcexcm or even less than 10 xcexcm.
Preferably, the coating is provided on the engaging surface that engages the face of the membrane which also forms an inner surface of the envelope, so that the sealing interface aids in the containment of the fluid. This surface will generally be provided on the frame member. Of course, both engaging surfaces may be provided with a coating.
The peripheral shape of the ring member, and also of the frame member, may be chosen as required. For example, the members may have a circular, oval, elliptical, or other closed curve, peripheral shape.
The frame member may comprise a rigid transparent window forming a wall of the envelope. The rigid window may be of any suitable material, for example glass, or a plastics material, such as polycarbonate. Indeed, for ease of manufacture, the frame member may be made entirely of such transparent material. Alternatively, the rigid window may form a part of the frame member, for example being bonded to and/or enclosed by an annular frame.
The frame member may be provided with a second engaging surface engaging a second membrane. In this case, a second ring member may be provided with a second engaging surface for engaging the second membrane. The second engaging surface may be opposed to the first engaging surface of the frame member. The second membrane may define a wall of the envelope.
Alternatively, the first ring member may be provided with a second engaging surface engaging a second membrane. Again, a second ring member may be provided with a second engaging surface for engaging the second membrane. The second engaging surface may be opposed to the first engaging surface of the first ring member. The second membrane may define a wall of the envelope.
The first and second membranes may be formed from a single membrane web, although preferably the first and second membranes are discrete.
A duct may be provided through a wall of the envelope, preferable a radially outer wall, which duct is in communication with the envelope. Such a duct will allow fluid to be removed from or introduced to the envelope in order that the volume and/or pressure of the fluid in the envelope may be varied to vary the power of the lens.
The duct may be formed by a pre-formed bore, or drilled, in one or more of the first or second ring members or the frame member.
The duct may be provided with suitable closure means to prevent leakage of fluid from the envelope through the duct. Such closure means may be as described in WO96/38744, or may be a rubber or elastomer bung penetrable by a needle of a syringe and capable of self-sealing on removal of the needle. Alternatively, a valve may be provided in the duct, arranged so that the duct is normally closed, but capable of being opened by, for example, the needle of a syringe. In one embodiment, the valve comprises a ball urged by a spring against an annular seat. To vary the pressure of fluid in the envelope, a needle of a syringe or similar is inserted through the centre of the seat, thus displacing the ball. Fluid can be then be introduced into or removed from the envelope to vary the pressure therein. When the needle is retracted, the spring urges the ball against the seat again to close the valve and seal the duct.
It has been found by the applicant that, with preferred transparent fluids such as silicone oil, which is relatively viscous, such a duct must be relatively large in order to enable efficient filling of the lens. One way in which the effective size of such a duct may be increased, is by providing a plurality of ducts in a wall of the envelope.
This in itself is believed to be new, and thus according to an invention disclosed herein, there is provided a variable focus lens comprising a transparent envelope at least partially defined by a flexible, transparent membrane and containing a transparent fluid, and a plurality of ducts provided in a wall of the envelope for introducing fluid into the envelope.
The plurality of ducts may be provided with respective closure means, for example as described above, or may be provided with a single closure means for a plurality of ducts. The ducts may be distributed about the periphery of the lens, but in a preferred arrangement the ducts are proximately grouped.
As an alternative to providing a plurality of ducts, it is possible to provide a single duct having a large cross-section. It will be appreciated that the maximum width of the duct in the direction of the axis of the lens is limited by the thickness of the wall of the envelope which forms the lens. However, the cross-sectional area of the duct can be increased by forming the duct such that its width perpendicular to the axis of the lens is greater than its width parallel to the axis of the lens.
The retaining means may be any suitable means, for example screws, clips and the like. Respective retaining means may be provided for each of said first and second ring members.
In a preferred arrangement, the retaining means take the form of a deformable portion of one of the frame member and the ring member, arranged to be deformed, for example crimped, over the other of the frame member and the ring member. In this case, the deformable portion may be of metal, such as aluminium, stainless steel or titanium.
Advantageously, the retaining means may be provided by a pair of spectacles or similar device, into which the lens is to be mounted.
The transparent fluid retained within the envelope may be any suitable fluid, for example silicone oil, such as 703 type silicone oil.
The fluid may be communicated to the envelope by means of a suitable pump, for example a syringe.
However, it has been realised by the applicant that a simple syringe is not ideal as a pump for varying the focus of the lens. One reason for this is that the plunger of the syringe is difficult to control accurately. For example, static friction between the piston and the syringe barrel must be overcome before the plunger moves, such that pressure applied to the plunger tends to build up until the static friction is overcome, at which point the plunger moves relatively rapidly.
Thus, according to an invention disclosed herein, there is provided a pump for a variable focus lens comprising a fluid chamber having an outlet port and a linearly movable member arranged to vary the effective volume of the fluid chamber, wherein locating means are provided for locating the movable member in a plurality of discrete positions.
In a simple arrangement the locating means may be in the form of two stops arranged to limit the movement of the movable member, for example a piston or plunger, to a range having end points defined by respective stops. The end points may correspond respectively to a first predetermined power of the lens, for example for the correction of myopia of a user, and a second predetermined power of the lens, for example for correction of hypermetropia or presbyopia of a user. In this way a bifocal lens may be produced which can be adjusted by the user for reading and close work or distance vision.
The stops may be variable in their positions, for example for initial setting of two levels of power for the lens, and may be lockable in a selected position.
The locating means may comprise a series of locators, for example teeth of a rack or the like, which may be engaged by a suitable mating member, in order that the movable member is adjustable step-wise.
It has also been found preferable by the applicant for users of variable focus lenses, for example users of spectacles incorporating variable focus lenses, to control the focus of the lenses by a rotational movement rather than a linear movement such as that of the piston of a syringe.
Thus, according to an invention disclosed herein, there is provided a pump for a variable focus lens comprising a fluid chamber having an outlet port and means for linearly varying the volume of the fluid chamber in response to a rotational movement of a control member.
The pump may comprise a pinion coupled for rotation with a control knob and engaging a rack coupled for linear movement to a piston provided in the fluid chamber. Alternatively, a piston received within the fluid chamber may be provided on a threaded shaft, the shaft engaging with a complementary threaded collar, such that the collar or the shaft may be rotated to cause the piston to move linearly within the fluid chamber. Alternatively, the interior of the fluid chamber may be threaded, and the periphery of the piston may be provided with a complementary thread such that rotation of the piston causes linear movement thereof within the fluid chamber.
In a presently preferred arrangement, a barrel member is provided having a threaded exterior, circumferential wall, and a fluid port defined in an end wall thereof. The barrel member is received within a cap member provided with a complementary interior thread and an end wall opposed to the end wall of the barrel member. The fluid chamber is defined by the volume enclosed by the connected barrel and cap members. According to this arrangement, as the cap member and barrel member are rotated relative to each other the cap moves away from or towards the end face of the barrel member, thereby linearly increasing or reducing the volume of the fluid chamber. The cap member may optionally be provided with a piston mounted in fixed relation to its end face and received within the barrel member. In this case, the fluid chamber is defined between the end face of the barrel member and the piston, and relative rotation of the barrel member and cap member causes the piston to reduce the effective volume of the fluid chamber.
Locating means as described above may be provided in the context of a rotational control member.
According to an invention disclosed herein, there is provided a variable focus lens in combination with a pump as described herein.
In a preferred arrangement, two variable focus lenses are provided in a spectacle frame. A single pump may be provided, although it is preferred for a respective pump to be provided for each lens, so that each lens is independently variable.
The pump(s) may be provided on the arms of the spectacle frames, for example at the ends of the arms, so that they are hidden by the ears in use.
Channels may be provided in the spectacle frame, for example in the arms, for fluid communication between the lenses and the pump(s).
The pump(s) may be arranged to be detachable from the spectacles, for example permanently detachable after an initial setting operation of the focus of the lenses. The pump(s) may be arranged to be detachable from the spectacles such that when the pump(s) is/are detached the fluid communication channels are automatically closed off, for example by means of a valve.
In a preferred embodiment, a pair of spectacles has two pumps, one for each lens, with each pump being removably attached to an arm of the spectacles. Fluid communication between each pump and its respective lens is achieved by means of flexible tubing extending from the pump to the lens. The flexible tubing is received in a channel in the frame of the spectacles for at least part of its length. When the user has set the focus of the lens, the tubing is closed and cut, and the pump and the portion of the tubing attached thereto is detached and discarded.
In one particularly preferred form, a part of the tubing connecting the lens and the pump is received in a channel formed in the main frame of the spectacles, preferably in the side facing the user. The tubing projects from this recess beyond the side of the spectacles to join the pump attached to the arm of the spectacles.
The tubing can be closed in any suitable manner. However, it is preferred for the tubing to be clamped closed, for example by means of a screw urging the sides of the tubing together. In a preferred form, a screw is provided in a passage in the frame of the spectacles, perpendicular to and intersecting the channel in which the tubing is received. On the opposite side of the channel from the screw is a member which extends across the channel in the form of a bridge. When it is desired to close the tubing, the screw is screwed into the passage, and the end of the screw compresses the tubing against the member to close it. The part of the tubing which projects beyond the end of the channel can then be removed, for example by cutting it so that its end lies flush with the side of the frame.
In a particularly preferred embodiment, the member is formed by a part of the hinge attaching the arm to the main frame. This helps to retain the tubing in the channel, and avoids the need to provide a separate member.
As an alternative, the tubing could be closed by compression means other than a screw. For example, the frame may be provided with a button, which when depressed compresses the tubing against a member to close it. The button may be arranged such that it latches when it is depressed, to ensure that the tubing remains closed. In addition, the button can be provided with means for retaining it in its original position, to prevent accidental operation. These means may take the form of a protuberance on the button, which fits into a corresponding recess in the frame.
In addition, means can be provided in the spectacles to allow the tubing to be cut. For example, a button carrying a blade may be provided, the blade severing the tubing when the button is depressed. This button may be provided separately; however, it is preferred that the button which closes the tubing and the button which cuts it are combined, so that the tubing can be closed and cut in a single movement. This simplifies the process of setting the spectacles to a desired focus.
As mentioned in WO96/38744, the lenses can be pre-filled with fluid during their manufacture. The pumps then need only contain a sufficient amount of fluid to allow the adjustment of the focus of the lenses.
It will be appreciated that it is very important for the lens to be completely filled with fluid, with no air bubbles in the lens. The presence of air bubbles is extremely distracting for the wearer of the spectacles.
A number of approaches can be taken to filling the lens so as to avoid the presence of air bubbles in the filled lens. For example, in one method which has proved effective, some of the air in the envelope of the lens is first sucked out, and then a similar amount of fluid is injected. The cycle of air removal followed by fluid injection is then repeated as necessary until the lens is filled with fluid.
In an alternative method, a needle whose external diameter is less than the internal diameter of the duct is used to inject the fluid. The gap between the needle and the needle allows air in the lens to escape as fluid is injected. Fluid can still be injected through the needle while it is being withdrawn from the duct.
It is also preferred for the fluid used to fill the lens to be degassed prior to filling, to reduce the chance of bubbles forming in the lens after filling.
Filling the lens will normally involve injection of a relatively viscous fluid through a narrow passageway. The filling process can be facilitated by heating the fluid prior to injection, so as to reduce its viscosity.
The variable focus lens described herein may be provided with at least one transparent, protective cover for the or each flexible membrane. The cover may be, for example, a rigid sheet of transparent material, for example glass or a plastics material such as polycarbonate. The protective cover may be mounted, for example bonded, to the ring member or the frame member.
As mentioned above it has been found by the applicant that in order to obtain a desired optical quality of a variable focus lens it is important that the membrane is maintained under tension. For this purpose it is advantageous to form the membrane from a heat-shrinkable plastics material.
Thus, according to an invention disclosed herein, there is provided a method of making a variable focus lens having a flexible, transparent membrane supported in a frame, wherein the membrane is heat treated while held in the frame to increase the tension in the membrane.
It has been found by the applicant that, at least with preferred materials for the membrane, e.g. Mylar, heat treatment of the membrane causes the membrane material to contract and thereby increase the tension in the membrane.
The membrane may be treated using any suitable source of heat, and in a preferred arrangement the heat is provided by a source of hot air, such as a hair dryer, a hot air gun or a fan heater.
According to an invention disclosed herein, there is provided a method of making a variable focus lens having a flexible, transparent membrane supported in a frame, wherein the membrane is pre-tensioned, and the frame is mounted to the membrane while the membrane is pre-tensioned. In this way, a convenient method of ensuring that the membrane is in tension on the frame is provided.
Any suitable means may be provided for pre-tensioning the membrane. For example, the principles for tensioning the membrane disclosed in GB 2184562 and 2183059 may be applied in this novel way to the pre-tensioning of the membrane.
The frame may be a frame as disclosed elsewhere herein.
The variable focus lens described above is of course suitable for use in spectacles. However, it can also be used on any form of eyewear where it may be desired to incorporate corrective optics, including but not limited to sunglasses, swimming goggles, skiing goggles, squash glasses, sports eyewear in general, welding masks, welding goggles, laboratory goggles, and protective eyewear in general. The lens may be provided as an insert, or may have means for attachment to the outside of the eyewear.
If the lens is to be used in sunglasses, then the material of the membranes or the fluid itself could be tinted. Further, it is possible to use metallized Mylar, which reflects a portion of the light incident thereon and transmits the remainder, as the material of the outer membrane, thereby providing reflective sunglasses.